Making nanocrystalline mesoporous spherical particles

Abstract

Spherical particles of one or more elemental metals and carbon are prepared from a precursor in the form of a metal oleate. The metal oleate precursor is dispersed in a liquid vehicle and aerosol droplets of the dispersed precursor are formed in a stream of an inert gas. The aerosol droplets are heated in the stream to decompose the oleate ligand portion of the precursor and form spherical particles that have a mesoporous nanocrystalline structure. The open mesopores of the spherical particles provide a high surface area for contact with fluids in many applications. For example, the mesopores can be infiltrated with a hydrogen absorbing material, such as magnesium hydride, in order to increase the hydrogen storage capacity of the particles.

The invention claimed is: 
     
       1. A method of making spherical particles that are a composite of one or more elemental metals, elemental carbon, and oxygen, the method comprising:
 forming a metal oleate precursor by reacting one or more metal oxides, metal acetates, metal acetylacetonates or metal inorganic salts of the one or more elemental metals with oleic acid; 
 forming a dispersion of the metal oleate precursor in a liquid vehicle; 
 forming aerosol droplets of the liquid vehicle-dispersed precursor in a flowing stream of an inert gas; and 
 heating the aerosol droplets in the stream to remove the liquid, decompose organic acid material, and form spherical particles of the one or more elemental metals, elemental carbon and oxygen having a uniform mesoporous nanocrystalline structure. 
 
     
     
       2. The method of making spherical particles as recited in  claim 1  further comprising:
 heating the aerosol droplets in the flowing stream for a sufficient amount of time so that nanocrystals of the one or more elemental metals form in the droplets, decomposed organic acid material is expelled from the droplets, and the nanocrystals become organized into a three-dimensional network and are uniformly attached by fine, elemental carbon particles. 
 
     
     
       3. The method of making spherical particles as recited in  claim 1  further comprising:
 filtering the spherical particles from the stream, and 
 heating the filtered particles in an atmosphere of an inert gas to remove residual organic material. 
 
     
     
       4. The method of making spherical particles as recited in  claim 1  wherein the one or more elemental metals are at least one of nickel and platinum. 
     
     
       5. The method of making spherical particles as recited in  claim 1  wherein the liquid vehicle is non-aqueous. 
     
     
       6. The method of making spherical particles as recited in  claim 1  wherein the liquid vehicle comprises tetrahydrofuran. 
     
     
       7. The method of making spherical particles as recited in  claim 1  wherein the aerosol droplets are heated to a temperature of about 550° C. 
     
     
       8. The method of making spherical particles as recited in  claim 1  wherein the molar concentration of the metal oleate precursor in the liquid vehicle is in the range of about 0.01 to about 0.5 mol/L. 
     
     
       9. The method of making spherical particles as recited in  claim 1  further comprising:
 forming particles of a metal hydride in mesopores of the spherical particles. 
 
     
     
       10. The method of making spherical particles as recited in  claim 1  further comprising:
 immersing the spherical particles in a solution of dibutylmagnesium; 
 removing the particles from the solution; and 
 heating and pressurizing the particles in an atmosphere of hydrogen gas to form magnesium hydride particles in mesopores of the spherical particles. 
 
     
     
       11. The method of making spherical particles as recited in  claim 9  or  10  further comprising:
 heating the spherical particles so that the hydride particles release hydrogen. 
 
     
     
       12. The method of making spherical particles as recited in  claim 1  in which the metal oleate precursor is formed by reacting one or more elemental metals with oleic acid by steps comprising:
 forming a metal oleate precursor by reacting one or more inorganic metal salts of the one or more elemental metals with oleic acid in a basic solution; 
 precipitating the metal oleate precursor from the solution; 
 separating the metal oleate precursor precipitate from any by-products.